Polyimides derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride, which produces heat resistant polyimides, are usually polyimides obtained using 3,3′,4,4′-biphenyltetracarboxylic dianhydride and paraphenylenediamine as the starting acid dianhydride component and starting diamine component, respectively, and these are known to yield polyimides with low linear thermal expansion coefficients and high elastic moduli.
Because films composed of such polyimides have excellent thermal and electrical properties, they are widely used in electronic devices. However, it is not possible to achieve high adhesive strength with adhesives that are usually used in the field of electronics, while laminated bodies comprising metal layers formed by metal vapor deposition or sputtering have relatively low peel strength.
The polyimide films also have low saturated absorption percentages and low hygroscopic expansion coefficients, and therefore provide an advantage of dimensional stability against environmental changes. Yet their relatively low moisture permeation rates tend to result in foaming or delamination at the metal-polyimide interfaces of laminated bodies manufactured by casting methods.
Conventional polyimide laminated bodies made of aromatic polyimide film layers and metal material layers, and processes for their manufacture, are described or suggested in Japanese Examined Patent Publication No. 59-18221, Japanese Unexamined Patent Publication No. 57-181857, Japanese Unexamined Patent Publication No. 62-212140 and Japanese Examined Patent Publication No. 1-52843.
There has also been proposed a polyimide composite sheet comprising a metal film layer and an aromatic polyimide film layer formed by casting an aromatic polyamic acid solution composition, obtained by polymerizing an aromatic tetracarboxylic acid component composed of a biphenyltetracarboxylic anhydride and a pyromellitic anhydride, and an aromatic diamine component composed of a phenylenediamine and a diaminodiphenyl ether, onto a metal thin-film and drying the film while accomplishing imidization at high temperature (see Japanese Unexamined Patent Publication No. 61-111359).
There has also been proposed a printed wiring substrate comprising a metal film layer and an aromatic polyimide film layer formed by casting an aromatic polyamic acid solution composition, obtained by polymerizing an aromatic tetracarboxylic acid component composed of a biphenyltetracarboxylic anhydride and a pyromellitic anhydride, and an aromatic diamine component composed of a phenylenediamine and a diaminodiphenyl ether, onto an alkali-etchable metal substrate, performing imidization and then etching the metal substrate (see Japanese Unexamined Patent Publication No. 3-85789).
In addition, a flexible printed wiring substrate has been proposed which comprises a metal film layer and a polyimide film layer formed by casting a polyamic acid solution composition obtained by polymerizing components containing an aliphatic tetracarboxylic anhydride and a diamine onto a metal substrate and imidizing it (see Japanese Unexamined Patent Publication No. 2004-358961), but excessive time is required for drying and imidization, and this results in poor productivity.